Rotary wing aircraft that employ digital fly by wire control systems have a different mode of operation when on the ground versus in flight. The aircraft needs to operate with flight control proportional control authority when in proximity to the ground when one of the wheels touches the landing surface, and in a rate command mode when the wheels are off the ground and the aircraft is flying. It is important for flight controls to be in the correct proportional mode of operation with trim following and pitch roll authority to cope with landing wind conditions particularly on slope landings to prevent control problems if there is an inaccurate sensing of the weight on wheels when landing. Detection of the transition from in air mode to ground mode requires a selected weight on the wheel that has contacted the ground. Detection of a landing condition versus an airborne condition of aircraft has traditionally been accomplished using a weight on wheels (“WOW”) switch. In a helicopter application, the WOW switch includes a mechanical micro switch positioned on each landing gear for redundancy. When the aircraft lands and when there is more than a certain amount of weight on the landing gear, the WOW switch triggers to signal that the aircraft flight control system is to be switched to the ground mode. It is difficult to provide a consistent trigger point value using the mechanical switch, since different components on the landing gear, such as shock absorbers, provide variability to the weight on wheels. The mechanical switch provides a discrete on/off result, however an analog value of weight would be more useful to modern digital aircraft. Further, the mechanical switch inherently contains moving parts and often a plastic housing, which are susceptible to malfunction and damage.
The gross weight (“GW”) and center of gravity (“CG”) are other important aircraft weight-related factors to consider, particularly when determining if the aircraft is safe for take-off. The GW is needed to determine expected fuel consumption and acceptable payload quantities, and for calculating the CG. Ensuring that the CG is within the aircraft's certified CG limits can prevent the aircraft from become unstable during flight, thus avoiding a stall and possible crash from CG issues. Proper aircraft CG location can also be used to reduce fuel consumption as the CG location affects the amount of fuel the aircraft burns. Current vehicle environments determine GW and CG calculations by use of external scales or manual calculations based on a predetermined empty weight and a calculated load from fuel, passengers, and cargo.
As weight related issues for aircraft are important, the art would be receptive to improvements in aircraft weight measurement systems.